The present invention relates to data processing systems and more specifically to peripheral device addressing techniques.
In a data processing system capable of providing service to a plurality of programs, and in which a plurality of peripheral devices are attached for data transfer with the processor, it is typically necessary in order to provide flexibility, to allow the programmer the use of logical names or addresses of peripheral devices to which it will communicate data without need to identify the physical peripheral device which it in fact will communicate with. Further for increased flexibility it is often necessary to allow the operator to reassign the correspondence between the logical address which he has picked and which he has related to a physical address or the actual peripheral number, to change it to address another physical peripheral. This may be required either because for example the peripheral device he is using becomes inoperative or because for example at some interim time, another programmer is utilizing the same physical peripheral device. The need for this flexibility is particularly evident and necessary in data processing systems which are among other things utilized to emulate another data processing system.
In the prior art, peripheral devices have been reassigned by means of hard wired switching techniques wherein, should the operator require that his program work with another physical peripheral device, he would actually, after mounting for example a tape in a tape peripheral device, change the switches in the host processor's console in order to provide a data path as required. In addition to requiring a fairly substantial amount of time to accomplish this, such reassignment control has not been as flexible as might be desired. Further, such, what may be termed mechanically switched control, has not been adequate in systems which are utilized to emulate another data processing system. Further the time required to mechanically switch such connection is not compatible with today's high speed systems.
Accordingly, it is an object of the invention to provide a flexible means included in a data processing system for affecting reassignment control of peripheral devices to logical addresses utilized in the computer programs operating in the data processing system.